1. Field of the Invention
The field of the invention is that of locks and more particularly the improvement of the security of cylinder locks.
2. Background of the Invention
The procedure of attempting to pick a cylinder lock involves a process whereby tools are introduced into the key channel whose purpose it is to adjust the cylinder pins or tumbler pins and at the same time exert a torsional or twisting moment on the cylinder itself.
The adjusting tool inserted into the key channel has the purpose of attempting to shift the tumbler or cylinder pins which are biased by internal springs to positions which correspond to their unlocked positions thus enabling the rotary cylinder to be turned.
The second tool has the purpose of applying a torsional or twisting moment to the cylinder core thereby clamping the cylinder and locking pins so that as each cylinder and corresponding locking pin is pushed to its unlocked position, the spring biased locking pin is clamped tight and is not allowed to return to its locking position. Thus, the cylinder pins may be unlocked one at a time until all have been released thereby improperly unlocking the lock.
U.S. Pat. No. 3,195,330, as well as Swiss Pat. No. 139,744 disclose rotary cylinder locks containing tumbler pins with corresponding recesses into which an obstructing element may fall if an attempt is made to pick the lock. In the U.S. patent, a core pin is disclosed with a recess into which an obstructing pin may be dropped permanently if an attempt is made to pick the lock. The disadvantage that must be accepted with this prior art device is that the lock becomes useless unless disassembled once the obstructing pin has dropped into position.
In the above enumerated Swiss Patent, auxiliary tumblers are used, into whose recesses locking or obstructing pins may drop, if a non-fitting skeleton key is used and the cylinder is rotated one step. With this apparatus it will not be possible with a skeleton key to bring all tumblers into the unlocked position. There will still remain gaps into which the auxiliary tumblers may drop and be able to latch the lock permanently closed until disassembled.
There has been a need for a lock which impedes picking but which may thereafter be utilized with a legitimate key without first disassembling the lock and resetting the obstruction pins.